.\"	$NetBSD: fdatasync.2,v 1.16 2008/04/30 13:10:51 martin Exp $
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.Dd October 25, 2003
.Dt FDATASYNC 2
.Os
.Sh NAME
.Nm fdatasync
.Nd synchronize the data of a file
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft int
.Fn fdatasync "int fd"
.Sh DESCRIPTION
The
.Fn fdatasync
function forces all modified data associated with the file descriptor
.Fa fd
to be flushed to stable storage.
.Pp
The functionality is as described for
.Xr fsync 2 ,
with the exception that file status information need not be synchronized,
which may result in a performance gain, compared to
.Xr fsync 2 .
This behaviour is commonly known as
.Bf -symbolic
synchronized I/O data integrity completion.
.Ef
.Sh RETURN VALUES
A value of 0 is returned on success.
Otherwise, a value \-1 is returned and
.Va errno
is set to indicate the error.
.Sh ERRORS
The
.Fn fdatasync
function will fail if:
.Bl -tag -width Er
.It Bq Er EBADF
The
.Fa fd
argument is not a valid file descriptor open for writing.
.It Bq Er EINVAL
This implementation does not support synchronized I/O for this file.
.It Bq Er ENOSYS
The
.Fn fdatasync
function is not supported by this implementation.
.El
.Pp
In the event that any of the I/O operations to be performed fail,
.Fn fdatasync
returns the error conditions defined for
.Xr read 2
and
.Xr write 2 ,
and outstanding I/O operations are not guaranteed to have been completed.
.Sh SEE ALSO
.Xr fsync 2 ,
.Xr open 2 ,
.Xr read 2 ,
.Xr write 2
.Sh STANDARDS
The
.Fn fdatasync
function conforms to
.St -p1003.1b-93 .
